Strategy for using exhaust stroke post-injection to elevate exhaust temperature for diesel particulate filter regeneration

ABSTRACT

An engine control system ( 28 ) causes combustion chambers ( 20 ) to be fueled during an engine cycle by a main injection ( 38 ) ending no later than substantially at the TDC between compression and expansion strokes of the cycle without any further injection of fuel during the expansion stroke, and then during the exhaust stroke of the cycle, by a post-injection ( 40 ) for elevating the temperature of the gases into a regeneration temperature range for regenerating a diesel particulate filter ( 36 ).

FIELD OF THE INVENTION

This invention relates generally to internal combustion engines forpropelling motor vehicles, particularly to diesel engines having dieselparticulate filters (DPF's) as after-treatment devices in their exhaustsystems.

BACKGROUND OF THE INVENTION

A known system for treating exhaust gases passing through an exhaustsystem of a diesel engine comprises a diesel oxidation catalyst (DOC)associated with a diesel particulate filter (DPF). The combination ofthese two after-treatment devices promotes chemical reactions in theexhaust gases and traps diesel particulate matter (DPM) as the gasesflow through the exhaust system from the engine, thereby preventingsignificant amounts of pollutants from entering the atmosphere.

A DPF requires regeneration from time to time in order to maintainparticulate trapping efficiency. Regeneration involves creatingconditions that will burn off trapped particulates whose uncheckedaccumulation would otherwise impair DPF effectiveness.

The creation of conditions for initiating and continuing regenerationgenerally involves elevating the temperature of exhaust gas entering theDPF to a suitably high temperature. Because a diesel engine typicallyruns relatively cool and lean, the post-injection of diesel fuel hasbeen used as part of a DPF regeneration strategy to elevate exhaust gastemperatures entering the DPF while still leaving excess oxygen forburning the trapped particulate matter.

When a vehicle is being operated in a way conducive to DPF regeneration,such as cruising on a highway, the regeneration process may be conductedwith little or no significant effect on vehicle driveability and may beinitiated either by the driver or else automatically by a regenerationinitiation strategy even before the DPF becomes loaded with DPM to anextent where forced regeneration would be mandated by the engine controlsystem.

The inventors have discovered that a “close” post-injection offuel—meaning an injection occurring during the expansion, or power,stroke within a range of about 60° after top dead center (ATDC)—makes acontribution to crankshaft torque having a sufficiently noticeableeffect on vehicle driveability that some drivers may considerobjectionable.

Compensating for the effect of “close” post injection in order tominimize its influence on vehicle drivability requires an extensivedevelopment effort in order to achieve the best possible calibration.One consideration that needs to be addressed is the ability of the fuelinjectors to deliver “close” post-injections immediately following maininjections. Certain fuel injectors that do possess desirable attributesmay nonetheless have difficulty in delivering a “close” post-injectionthat is needed too soon after a main injection. The difficulty becomesmore pronounced as engine speed increases into a high speed range.

While use of a “far” post-injection during the expansion stroke—meaningan injection occurring during later than a “close” post-injection—mayaddress any issue of a fuel injector's ability to deliver apost-injection at a desired time during the expansion stroke, apost-injection that is too “far” in the expansion stroke may causesignificant cylinder wall washing that can lead to motor oil dilution.

These discoveries and recognitions have led the inventors to seek analternative and better solution for using post-injection to elevateexhaust temperature to levels for initiating and maintaining DPFregeneration.

SUMMARY OF THE INVENTION

The present invention relates to a novel strategy that provides such asolution.

In contrast to seeking an optimum calibration for post-injection byrepeatedly initiating regeneration using different post-injectionquantities and timings within a timing range immediately after TDC inthe expansion stroke and then evaluating the results to ascertain anoptimum, the inventors have discovered that a post-injection late in theexhaust stroke can be just as effective in initiating and maintainingDPF regeneration, with lesser affect on vehicle driveability and withoutrequiring as extensive a development effort, as when “close”post-injection during the expansion stroke is used. Moreover, theinvention avoids issues concerning the ability of a fuel injector todeliver a post-injection in close proximity to a main injection (therebyavoiding injector and/or injector driver and control modifications) andissues concerning excessive cylinder wall washing contributing to motoroil dilution.

Delaying post-injection to a time within a range spanning a laterportion of the exhaust stroke has been found to create neither thepotentially objectionable torque rise mentioned above nor objectionablecylinder wall washing while in doing so, giving fuel injectors,particularly hydraulically-driven ones, time to “re-charge” between themain injection and providing the same effect as “close” (expansionstroke) post-injection for initiating and maintaining DPF regeneration.

The invention can be implemented in existing systems through appropriatemodifications of processor algorithms that control timing of fuelinjections. Hence, no additional hardware is needed. Optimum timingduring the exhaust stroke can be developed by calibration adjustmentduring driveability testing with lesser effort than that required when“close” (expansion stroke) post-injection is used.

Accordingly, one generic aspect of the present invention relates to adiesel engine comprising a fueling system for injecting diesel fuel intocombustion chambers where the fuel combusts to power the engine, anexhaust system through which gases created by combustion pass toatmosphere and which comprises an after-treatment device that treats thegases before leaving the exhaust system but at times requiresregeneration by elevation of temperature of the gases to a regenerationtemperature range, and an engine control system for processing variousdata to control various aspects of engine operation including fuelingperformed by the fueling system and regeneration of the after-treatmentdevice.

In consequence of a regeneration request, the control system causes thefueling system to fuel the combustion chambers during an engine cyclefor a combustion chamber by a main injection ending no later thansubstantially at the TDC between compression and expansion strokes ofthe cycle without any further injection of fuel during the expansionstroke, and then during the exhaust stroke of the cycle, by apost-injection for elevating the temperature of the gases into theregeneration temperature range.

Another generic aspect relates to a motor vehicle powered by an engineas just described.

Still another generic aspect relates to a method for initiatingregeneration of an exhaust gas after-treatment device in an exhaustsystem of a diesel engine having a fueling system for injecting dieselfuel into combustion chambers where the fuel combusts to power theengine and an engine control system for processing various data tocontrol various aspects of engine operation including fueling performedby the fueling system and regeneration of the after-treatment device.

The method comprises initiating regeneration by causing the fuelingsystem to fuel the combustion chambers during an engine cycle for acombustion chamber by a main injection ending no later thansubstantially at the TDC between compression and expansion strokes ofthe cycle without any further injection of fuel during the expansionstroke, and then during the exhaust stroke of the cycle, by apost-injection.

The foregoing, along with further features and advantages of theinvention, will be seen in the following disclosure of a presentlypreferred embodiment of the invention depicting the best modecontemplated at this time for carrying out the invention. Thisspecification includes drawings, now briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic diagram of an exemplary internalcombustion engine embodying a strategy for initiating and maintainingDPF regeneration in accordance with principles of the present invention.

FIG. 2 is a fuel injection timing diagram illustrating the strategy.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an example of a turbocharged diesel engine 10 having anintake system 12 through which charge air enters and an exhaust system14 through which exhaust gas resulting from combustion exits, not alldetails of those two systems that are typically present being included.When used in a motor vehicle, such as a truck, engine 10 is coupledthrough a drivetrain 16 to driven wheels 18 that propel the vehicle.

Engine 10 comprises cylinders 20 forming combustion chambers into whichfuel is injected by fuel injectors 22 to combust with the charge airthat has entered through intake system 12. Energy released by combustionpowers the engine via pistons 24 connected to a crankshaft 26 leading todrivetrain 16 for propelling the vehicle.

Fuel injectors 22 are under the control of an engine control system 28that comprises one or more processors that process various data todevelop data for controlling various aspects of engine operationincluding controlling pressure of hydraulic fluid supplied to fuelinjectors 22 (reference numeral 30) and the timing of operation of valvemechanisms in the fuel injectors that use the hydraulic fluid to forcefuel out of the injector tips into the combustion chambers.

Intake valves 32 control the admission of charge air into cylinders 20,and exhaust valves 34 control the outflow of combustion gases throughexhaust system 14 and ultimately to atmosphere. Before entering theatmosphere however, the combustion gases are treated by one or moreafter-treatment devices. The one device shown here with which thepresent invention is concerned is a diesel particulate filter, or DPF,36.

Various sensors are associated with the after-treatment devices forproviding information to control system 28. One piece of information isthe extent to which DPF 36 is loaded with particulates. Control system28 contains algorithms that are repeated executed to process certaindata for various control purposes. One such algorithm uses informationabout DPF particulate loading to initiate regeneration when conditionsare suitable even if the DPF is loaded below a level requiring forcedregeneration and to force regeneration when the DPF becomes loaded tothe level calling for forced regeneration.

With engine 10 running, a main fuel injection occurs substantially atTDC between the compression stroke C and expansion, or power, stroke P,as represented by the injection 38 in FIG. 2 illustrating conventionaldiesel (CD) combustion.

When control system 28 requests regeneration of DPF 36, main injectionssuch as 38 continue, but now a specific post-injection strategy isemployed.

That strategy employs no post-injection during the expansion stroke, butrather a post-injection during the exhaust stroke E, preferably during atime toward the end of the exhaust stroke but ahead of the TDC thatoccurs between the end of the exhaust stroke and the beginning of thenext intake stroke I, as represented by the post-injection 40 in FIG. 2.

The strategy continues until regeneration is initiated and alsothereafter in order to maintain regeneration. When the strategyterminates regeneration, the post-injection during the exhaust strokeconcludes.

Certain diesel engines are at times capable of operating by alternativediesel combustion, as distinguished from CD combustion, and while theengine that has been described here operates by CD combustion, it isbelieved that principles of the invention are applicable to an enginerunning by alternative diesel combustion provided that the controlsystem allows DPF regeneration while the engine is so running.Alternative diesel combustion is a generic term for certain processesand systems such as Homogeneous Charge Compression Ignition (HCCI),Controlled Auto-Ignition (CAI), Dilution Controlled Combustion Systems(DCCS), and Highly Premixed Combustion Systems (HPCS). When an engine isrunning by an alternative diesel combustion process, the effect ofwhatever injections occur until main combustion occurs may be consideredequivalent to a main injection of CD combustion.

It should also be understood that the use of post-injection during theexhaust stroke instead of during the expansion stroke may be only oneelement of a more comprehensive regeneration strategy that uses otherthan merely fuel injection to initiate and maintain DPF regeneration.

While a presently preferred embodiment of the invention has beenillustrated and described, it should be appreciated that principles ofthe invention apply to all embodiments falling within the scope of thefollowing claims.

1. A diesel engine comprising: a fueling system for injecting dieselfuel into combustion chambers where the fuel combusts to power theengine; an exhaust system through which gases created by combustion passto atmosphere and which comprises an after-treatment device that treatsthe gases before leaving the exhaust system but at times requiresregeneration by elevation of temperature of the gases to a regenerationtemperature range; an engine control system for processing various datato control various aspects of engine operation including fuelingperformed by the fueling system and regeneration of the after-treatmentdevice; wherein in consequence of a regeneration request, the controlsystem causes the fueling system to fuel the combustion chambers duringan engine cycle for a combustion chamber by a main injection ending nolater than substantially at the TDC between compression and expansionstrokes of the cycle without any further injection of fuel during theexpansion stroke, and then during the exhaust stroke of the cycle, by apost-injection for elevating the temperature of the gases into theregeneration temperature range.
 2. A diesel engine as set forth in claim1 wherein the post-injection is caused to occur nearer TDC than BDC. 3.A diesel engine as set forth in claim 1 wherein the main injectioncauses the engine to operate by conventional diesel combustion.
 4. Adiesel engine as set forth in claim 1 wherein the after-treatment devicecomprises a diesel particulate filter.
 5. A diesel engine as set forthin claim 4 wherein the post-injection is caused to occur nearer TDC thanBDC.
 6. A motor vehicle comprising: a diesel engine for turning drivenwheels through a drivetrain to propel the vehicle: a fueling system forinjecting diesel fuel into combustion chambers of the engine where thefuel combusts to propel the vehicle; an exhaust system through whichgases created by combustion pass to atmosphere and which comprises anafter-treatment device that treats the gases before leaving the exhaustsystem but at times requires regeneration by elevation of temperature ofthe gases to a regeneration temperature range; an engine control systemfor processing various data to control various aspects of engineoperation including fueling performed by the fueling system andregeneration of the after-treatment device; wherein in consequence of aregeneration request, the control system causes the fueling system tofuel the combustion chambers during an engine cycle for a combustionchamber by a main injection ending no later than substantially at theTDC between compression and expansion strokes of the cycle without anyfurther injection of fuel during the expansion stroke, and then duringthe exhaust stroke of the cycle, by a post-injection for elevating thetemperature of the gases into the regeneration temperature range.
 7. Amotor vehicle as set forth in claim 6 wherein the post-injection iscaused to occur nearer TDC than BDC.
 8. A motor vehicle as set forth inclaim 6 wherein the main injection causes the engine causes the engineto operate by conventional diesel combustion.
 9. A motor vehicle as setforth in claim 6 wherein the after-treatment device comprises a dieselparticulate filter.
 10. A motor vehicle as set forth in claim 9 whereinthe post-injection is caused to occur nearer TDC than BDC.
 11. A methodfor initiating regeneration of an exhaust gas after-treatment device inan exhaust system of a diesel engine having a fueling system forinjecting diesel fuel into combustion chambers where the fuel combuststo power the engine and an engine control system for processing variousdata to control various aspects of engine operation including fuelingperformed by the fueling system and regeneration of the after-treatmentdevice, the method comprising: initiating regeneration by causing thefueling system to fuel the combustion chambers during an engine cyclefor a combustion chamber by a main injection ending no later thansubstantially at the TDC between compression and expansion strokes ofthe cycle without any further injection of fuel during the expansionstroke, and then during the exhaust stroke of the cycle, by apost-injection.
 12. A method as set forth in claim 11 comprising causingthe post-injection to occur nearer TDC than BDC.
 13. A method as setforth in claim 11 comprising injecting the main injection so as to causethe engine to operate by conventional diesel combustion.